Conventionally, in the filtration of water such as seawater, lake water, river water, water in a water supply, and water in a sewerage system, the filtration of liquid for general industrial use such as cooling water for various devices or process liquid, and the filtration of gas and the like of various raw materials for use in a chemical plant or the like, various filtration devices have been used for the purpose of trapping and removing fine particles, dust, and the like contained therein.
When a filtration device as mentioned above is operated for filtration for a long period, solid matter, gel dust, and the like are trapped and accumulated in the filter element, so that resistance for the fluid to pass through a filter medium increases, and this makes it difficult to filter target fluid in the end. In order to cope with this problem, for example, a process called “backwashing” is carried out periodically, in which fluid is made to pass through the filter element in a direction opposite to the flow direction for filtration, to remove trapped substances adhering to the filter element in order to restore filtration performance of the filter element. This method called “backwashing” is an excellent method capable of reducing filter-passing resistance to approximate the initial passing resistance easily without demounting the filter. In particular, in the case of a filtration device provided with a dedicated backwashing channel (a backwash pipe and a backwash fluid drain pipe), it is advantageous in that backwashing can be carried out without interrupting the filtration.
As such a filtration device capable of carrying out “backwashing,” there is a filtering apparatus including: an inlet for fluid to be filtered; an outlet for filtered fluid; a number of parallel filter elements, each of which is open at both ends and into which the fluid to be filtered is sent so that infiltration toward the outside of the element through the element will occur; and at least one washing mechanism connected alternately to different ends of each filter element among both ends of the filter element, wherein the washing mechanism forms a discharge channel for backwash of the elements generated by the pressure of a filtered flow, and each of the filter elements is divided into two parts between the ends so that the washing mechanism connected to each end of the element will cause backflushing only to a certain part of the length of the element at a time (for example, see Patent Document 1).
Further, there is a similar filtration device including: an inlet for fluid to be filtered; an outlet for filtered fluid; a number of parallel filter elements, each of which is open at both ends; and a washing mechanism connected alternately to different ends of each element among both ends of the filter elements, wherein the washing mechanism forms a discharge channel for backwash of the elements generated by the pressure of a filtered fluid (for example, see Patent Document 2).